Our invention comprises improvements in a synchronizer clutch assembly for a manual transmission such as the synchronizer clutch assemblies disclosed in prior art U.S. Pat. Nos. 2,221,900 and 3,366,208, which are assigned to the assignee of our present invention. It is an improvement also in the synchronizer assembly disclosed in pending patent application Ser. No. 08/116,780, filed Sep. 3, 1993, by Keith Roberts and Jonathan Larsen, two of the co-inventors in the present application. The copending application also is assigned to the assignee of the present invention.
Synchronizer clutch assemblies for manual transmissions typically include an intermediate torque transfer shaft situated between a torque input shaft and a transmission torque output shaft. Located in parallel disposition with respect to the intermediate shaft is a cluster gear assembly. Torque delivery gears of different pitch diameter may be journalled on the intermediate shaft, and a synchronizer clutch assembly is disposed adjacent one of the gears or between two adjacent gears. The synchronizer clutch assembly functions to drivably connect the torque delivery gears for rotation in unison or to connect one or both of the gears selectively to the intermediate shaft. The synchronizer clutch assembly synchronizes rotary motion of the gears, one with respect to the other, or rotary motion of one or both of the gears selectively with respect to the intermediate shaft prior to the establishment of a driving connection between the rotary members.
The previously described '900 patent includes a synchronizer clutch hub that is splined to the intermediate shaft at a location between two gears of different pitch diameter. A clutch sleeve with internal clutch teeth is mounted for axial sliding movement on the synchronizer hub. The gear to be synchronized with respect to the shaft carries external clutch teeth as well as an external clutch surface. A synchronizer clutch blocker ring of that prior art design is disposed between the sleeve and the external clutch teeth of the gear. The blocker ring is formed with an internal cone surface adapted to engage the external cone surface of the gear.
Thrust bars arranged within the sleeve of the prior art designs are engageable with the synchronizer ring when the clutch sleeve is moved toward the engaged position. A detent force created by detent elements on the thrust bars and the clutch sleeve creates a synchronizer blocker ring clutch engaging force that causes the blocker ring to index angularly with respect to the clutch hub. This indexing motion is established by a lost motion connection between the blocker ring and the clutch hub.
Chamfered external blocker ring teeth formed on the blocker ring are in axial alignment with chamfered ends on the internal clutch sleeve teeth. When the chamfered ends on the teeth of the blocker ring and the sleeve engage, a clutch engaging force is established that causes synchronism in the motion of the gear with respect to the intermediate shaft. When synchronism is established, the sleeve may be moved through the blocker ring teeth into engagement with the external gear teeth with a smooth engaging action.
The detent force that is created upon initial movement of the sleeve in the construction of the '900 patent is established by a spring force acting in a radial direction on the thrust bars. The overall clutch assembly including the thrust bars, the springs, the sleeve and the synchronizer blocker ring is a relatively complex construction and inherently is more costly than a clutch assembly that does not require synchronizing action, such as positive drive dog clutch teeth.
Prior art patent '208 has features that are common to prior art patent '900, but it includes a pair of clutches rather than the single cone clutch. That design establishes greater synchronizer blocker ring clutch torque for a given degree of axially directed force on the synchronizer clutch sleeve. The basic design of the synchronizer clutch of the '208 patent, however, still requires a relatively costly and complex manufacturing and assembly procedure that is common to the design of the '900 patent since it too includes thrust bars and radial springs for loading the thrust bars.
Both the design of the '208 patent and the design of the '900 patent require costly precision machining. This is true also of prior art U.S. Pat. No. 3,414,098, as well as other prior art synchronizer clutch designs typically used in a manual transmission for an automotive vehicle.